I can name 2 aliens conspiracies that have roots in some deeply racist shit.

Ancient Aliens are one. It's not a coincidence that basically the only thing in western Europe that you'd ever hear connected to that is Stonehenge. Because apparently it's unbelievable that a bunch of Africans could stack some rocks very high to make a pyramid or that a bunch of South Americans in Peru could make some lines in the desert, must be aliens. But Romans building the colosseum around the same time? Completely normal, no alien help needed. And that's before we get into the predecessors of that whole thing - from Nazi historians pretending to find Aryans everywhere and saying that they actually built all the stuff, to Andrew Jackson claiming that native americans weren't native to the land and that's why they need to be genocided. This idea that foreigners didn't actually achieve anything and it was thanks to outside help is deeply rooted in racism.

Another conspiracy theory deeply rooted in racism is the good old lizard people thing. A group of people controlling the world, where have I heard that before? Now the guy who started it, David Icke, insists that alien lizard people isn't just him saying jews without saying it. But considering he believes Protocols of the Elders of Zion is true and he wrote a book blaming 9/11 on Israel, I seriously doubt that.